Combined pitch and forward thrust control for unmanned aircraft systems

ABSTRACT

An aircraft control system for an unmanned aircraft comprising a forward propulsion system comprising a forward thrust engine and a vertical propulsion system comprising a vertical thrust engine. The aircraft control system may include a controller comprising an input coupled to receive a velocity signal indicating a determined amount of forward velocity and being configured to generate a pitch angle command associated with the determined amount of forward velocity; a splitting block comprising an input to receive the pitch angle command and being configured to generate a second pitch angle command and a forward thrust engine throttle command based on a bounded pitch angle for the unmanned aircraft; and an output coupled to provide the second pitch angle command to the vertical propulsion system and the forward thrust engine throttle command to the forward propulsion system.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional application and claims the benefit ofU.S. application Ser. No. 15/131,944, filed on Apr. 18, 2016, all ofwhich are incorporated herein by reference in their entirety.

TECHNICAL FIELD

The disclosed technology relates generally to aircraft control systems,and more particularly, some embodiments relate to combining forwardthrust control of a multirotor vertical propulsion system with thrustcontrol of the forward propulsion system to control the aircraft inhovering flight across a wide range of air speeds.

DESCRIPTION OF THE RELATED ART

Unmanned aircraft have become ubiquitous in today's society. Theirimportance and value has grown dramatically in recent years, leading towidespread adoption in commercial, military and consumer market sectors.Part of the reason for their popularity is their low cost and small formfactor as compared to piloted aircraft. However, the small engines usedin various Unmanned Aircraft Systems (UAS) have demonstrated a lowerreliability as compared to piloted aviation engines.

Hybrid aircraft use a combination of vertical takeoff and landing (VTOL)propulsion systems to allow the aircraft to take off and land vertically(e.g., like a helicopter) and forward propulsion systems for fixed-wingflight. A hybrid quadrotor aircraft, for example uses four VTOL rotorsand one or more forward propulsion rotors. Quadrotor, octorotor, andother multirotor configurations for the VTOL propulsion system arepopular because they allow attitude control as well as control ofangular acceleration, rate, and even aircraft velocity and position.That is, flight dynamics can be controlled by individually controllingthe motor power or RPM of each rotor to control the torque on theaircraft.

With a standard multirotor control, the aircraft must pitch forward inorder to achieve positive acceleration. While this may be acceptable fornon-fixed-wing aircraft, it is undesirable in hybrid multirotor aircraftbecause a negative angle of attack of the fixed wing under conditions ofmore than minimal airspeed would cause a downward force on the aircraft.This would require the VTOL propulsion system to provide additionalthrust to maintain altitude and would add further drag to the aircraft.This further drag would, in turn, require additional forward tilt forcompensation.

Existing hybrid multirotor designs separate the functions of VTOL flightand forward acceleration into fixed wing flight. During VTOL operations,the VTOL rotors are controlled using a typical multirotor method, whichmay include pitching forward to increase forward speed. Duringacceleration to fixed wing flight as well as during fixed wing flight,the forward thrust rotor is used to accelerate the aircraft. Thisscheme, however, does not provide adequate control of the aircraftduring hovering modes in which a non-trivial airspeed is required, suchas hovering in windy conditions.

Hybrid aircraft control systems typically separate control the pitchangle and control of forward engine thrust. With such configurations,however, the integrators may end up fighting each other to achievestable control, but at a reduced efficiency. For example, a large pitchup command combined with a large forward thrust may result in stableposition control, but both systems are working harder than desired.

BRIEF SUMMARY OF EMBODIMENTS

According to various embodiments of the disclosed technology systems andmethods for pitch angle forward thrust of an aircraft is combined withforward thrust of the main fixed-wing engine or engines to allow controlof forward velocity of the aircraft. In some embodiments, this can beimplemented so as to allow the aircraft remain level in hovering flightacross a wide range of air speeds.

According to an embodiment of the disclosed technology, an unmannedaircraft may include: a forward propulsion system comprising a forwardthrust engine and a first rotor coupled to the forward thrust engine; avertical propulsion system that includes a vertical thrust engine and asecond rotor coupled to the vertical thrust engine; and a pitch angleand throttle control system. The pitch angle and throttle control systemmay include: a controller comprising an input coupled to receive avelocity signal indicating a determined amount of forward velocity andbeing configured to generate a pitch angle command associated with thedetermined amount of forward velocity; a splitting block comprising aninput to receive the pitch angle command and being configured togenerate a second pitch angle command and a forward thrust enginethrottle command based on a bounded pitch angle for the aircraft; anoutput coupled to provide the second pitch angle command to the verticalpropulsion system and the forward thrust engine throttle command to theforward propulsion system.

The splitting block in various embodiments may include a processorconfigured to perform the operations of comparing a determined boundedpitch angle for the aircraft to the pitch angle corresponding to thepitch angle command; generating a reduced pitch angle command so theresultant aircraft pitch angle does not exceed the bounded pitch angle;and generating the forward thrust engine throttle command based on thereduced pitch angle command.

Generating the forward thrust engine throttle command based on thereduced pitch angle command may include: determining a forward velocitygenerated by the limited pitch angle command; determining a differencein forward velocity between forward velocity generated by the limitedpitch angle and the determined amount of forward velocity; generating aresidual pitch angle command based on the determined difference inforward velocity; and converting the residual pitch angle command to theforward thrust engine throttle command.

The residual pitch angle command may be of a magnitude estimated toprovide sufficient forward thrust to account for the determineddifference in forward velocity. The determined amount of forwardvelocity may include a velocity error between a desired aircraftvelocity and an actual aircraft velocity. The velocity signal mayinclude a velocity error signal.

The controller may include proportional-integral-derivative (PID)controller to provide the forward thrust pseudo-control in the timedomain.

The thrust pitch angle command may be given by:

${PitchAngle} = {{K_{p}{e(t)}} + {K_{i}{\int{{e(t)}{dt}}}} + {K_{d}\frac{de}{dt}}}$where the e represents the velocity error.

In some embodiments, providing the second pitch angle command to thevertical propulsion system may include converting the second pitch anglecommand to a VTOL rotor command and providing the VTOL rotor command tothe vertical propulsion system.

The unmanned aircraft may be a multirotor aircraft and the verticalpropulsion system may include a plurality of vertical thrust engines andcorresponding rotors. In further embodiments, the unmanned aircraft maybe a hybrid quadrotor aircraft.

The bounded pitch angle may include a maximum pitch angle, or a range ofpitch angles between a minimum pitch angle and a maximum pitch angle.

In yet another embodiment, an unmanned aircraft system, may include anunmanned aircraft and a remote control system. The unmanned aircraft,may include: a forward propulsion system comprising a forward thrustengine and a first rotor coupled to the forward thrust engine; avertical propulsion system comprising a vertical thrust engine and asecond rotor coupled to the vertical thrust engine; an onboard aircraftcontroller comprising a first output coupled to the forward propulsionsystem and a second output coupled to the vertical propulsion system;and a first communication transceiver coupled to the aircraft controllerconfigured to communicate with a remote control system. The remotecontrol system, may include: a second communication transceiverconfigured to communicate with the unmanned aircraft; an aircraftcontrol system communicatively coupled to the second communicationtransceiver; and a pitch angle and throttle control system, comprising aprocessor configured to receive a velocity signal indicating adetermined amount of forward velocity and being configured to generate apitch angle command associated with the determined amount of forwardvelocity; receive the pitch angle command and being configured togenerate a second pitch angle command and a forward thrust enginethrottle command based on a bounded pitch angle for the aircraft; andprovide the second pitch angle command to the vertical propulsion systemand the forward thrust engine throttle command to the forward propulsionsystem.

In various embodiments, the pitch angle and throttle control system maybe part of the onboard aircraft controller or the aircraft controlsystem of the remote control system.

In yet another embodiment, an unmanned aircraft, may include a forwardpropulsion system comprising a forward thrust engine and a first rotorcoupled to the forward thrust engine; a vertical propulsion systemcomprising a vertical thrust engine and a second rotor coupled to thevertical thrust engine; and a pitch angle and throttle control system,comprising a processor configured to receive a first pitch anglecommand; and generate a second pitch angle command and a forward thrustengine throttle command based on a bounded pitch angle for the aircraft.The processor may further perform the operations of comparing adetermined bounded pitch angle for the aircraft to the pitch anglecorresponding to the first pitch angle command; generating a reducedpitch angle command so the resultant aircraft pitch angle does notexceed the bounded pitch angle; and generating the forward thrust enginethrottle command based on the reduced pitch angle command.

Generating the forward thrust engine throttle command based on thereduced pitch angle command may include determining a residual amount offorward thrust needed to compensate for the reduced pitch angle commandand generating the forward thrust engine throttle command to at leastpartially provide the residual amount of forward thrust needed. In otherembodiments, generating the forward thrust engine throttle command basedon the reduced pitch angle command may include: determining a forwardvelocity generated by the limited pitch angle command; determining adifference in forward velocity between forward velocity generated by thelimited pitch angle and the determined amount of forward velocity;generating a residual pitch angle command based on the determineddifference in forward velocity; and converting the residual pitch anglecommand to the forward thrust engine throttle command. The residualpitch angle command may be of a magnitude estimated to providesufficient forward thrust to account for the determined difference inforward velocity.

In some embodiments the processor may further perform the operationsincluding comparing a determined bounded pitch angle for the aircraft tothe pitch angle corresponding to the first pitch angle command;generating a reduced pitch angle command so the resultant aircraft pitchangle does not exceed the bounded pitch angle; generating a residualpitch angle command based on a difference between the first pitch anglecommand and the reduced pitch angle command; and converting the residualpitch angle command into a forward thrust throttle command.

The processor may further perform the operations including receiving avelocity signal indicating a determined amount of forward velocity andgenerating the pitch angle command to provide the determined amount offorward velocity. The determined amount of forward velocity may includea velocity error between a desired aircraft velocity and an actualaircraft velocity.

The processor may further perform the operations of converting thesecond pitch angle command to a VTOL rotor command and providing theVTOL rotor command to the vertical propulsion system.

In still further embodiments, a method of controlling forward thrust ofan aircraft includes: receiving a first pitch angle command; andgenerating a second pitch angle command and a forward thrust enginethrottle command based on a bounded pitch angle for the aircraft. Themethod may further include comparing a determined bounded pitch anglefor the aircraft to the pitch angle corresponding to the first pitchangle command; generating a reduced pitch angle command so the resultantaircraft pitch angle does not exceed the bounded pitch angle; andgenerating the forward thrust engine throttle command based on thereduced pitch angle command. In some embodiments, generating the forwardthrust engine throttle command based on the reduced pitch angle commandmay include determining a residual amount of forward thrust needed tocompensate for the reduced pitch angle command and generating theforward thrust engine throttle command to at least partially provide theresidual amount of forward thrust needed.

In other embodiments, generating the forward thrust engine throttlecommand based on the reduced pitch angle command may include:determining a forward velocity generated by the limited pitch anglecommand; determining a difference in forward velocity between forwardvelocity generated by the limited pitch angle and the determined amountof forward velocity; generating a residual pitch angle command based onthe determined difference in forward velocity; and converting theresidual pitch angle command to the forward thrust engine throttlecommand.

The method may further include comparing a determined bounded pitchangle for the aircraft to the pitch angle corresponding to the firstpitch angle command; generating a reduced pitch angle command so theresultant aircraft pitch angle does not exceed the bounded pitch angle;generating a residual pitch angle command based on a difference betweenthe first pitch angle command and the reduced pitch angle command; andconverting the residual pitch angle command into a forward thrustthrottle command.

The method may also include receiving a velocity signal indicating adetermined amount of forward velocity and generating the pitch anglecommand to provide the determined amount of forward velocity. Thedetermined amount of forward velocity may include a velocity errorbetween a desired aircraft velocity and an actual aircraft velocity.Also, the velocity signal may include a velocity error signal.

The method may also include converting the second pitch angle command toa VTOL rotor command and providing the VTOL rotor command to thevertical propulsion system.

Other features and aspects of the disclosed technology will becomeapparent from the following detailed description, taken in conjunctionwith the accompanying drawings, which illustrate, by way of example, thefeatures in accordance with embodiments of the disclosed technology. Thesummary is not intended to limit the scope of any inventions describedherein, which are defined solely by the claims attached hereto.

BRIEF DESCRIPTION OF THE DRAWINGS

The technology disclosed herein, in accordance with one or more variousembodiments, is described in detail with reference to the followingfigures. The drawings are provided for purposes of illustration only andmerely depict typical or example embodiments of the disclosedtechnology. These drawings are provided to facilitate the reader'sunderstanding of the disclosed technology and shall not be consideredlimiting of the breadth, scope, or applicability thereof. It should benoted that for clarity and ease of illustration these drawings are notnecessarily made to scale.

Some of the figures included herein illustrate various embodiments ofthe disclosed technology from different viewing angles. Although theaccompanying descriptive text may refer to such views as “top,” “bottom”or “side” views, such references are merely descriptive and do not implyor require that the disclosed technology be implemented or used in aparticular spatial orientation unless explicitly stated otherwise.

FIG. 1 illustrates an example unmanned vertical take-off and landing(VTOL) aircraft with which embodiments of the technology disclosedherein may be implemented.

FIG. 2 is a diagram illustrating an example unmanned aircraft with whichembodiments of the technology disclosed herein may be implemented.

FIG. 3 is a diagram illustrating an example process for combined pitchand forward thrust control in accordance with one embodiment of thesystems and methods described herein.

FIG. 4 is a diagram illustrating an example control loop combined pitchand forward thrust control in accordance with one embodiment of thesystems and methods described herein.

FIG. 5 illustrates an example splitting function in accordance with oneembodiment of the systems and methods described herein.

FIG. 6 illustrates an example process for generating pitch angle andforward thrust commands in accordance with one embodiment of the systemsand methods described herein.

The figures are not intended to be exhaustive or to limit the inventionto the precise form disclosed. It should be understood that theinvention can be practiced with modification and alteration, and thatthe disclosed technology be limited only by the claims and theequivalents thereof.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Embodiments of the technology disclosed herein are directed towarddevices and methods for providing a control scheme for an unmannedaircraft system in which the forward thrust control of a multirotor VTOLpropulsion system (i.e., pitch angle) is combined with forward thrustcontrol of the main fixed-wing forward propulsion system. Furtherembodiments can be configured to provide this combined control to allowthe aircraft to remain level in hovering flight across a wide range ofairspeeds. Embodiments of this combined control may be used in a numberof aircraft modes including in the strict hovering mode and intransition or a modes when the aircraft is transitioning from forwardflight to vertical landing.

In various embodiments, this combined control may be achieved byabstracting the forward thrust control command into a pseudo-control,which is then split into pitch angle and engine thrust commandcomponents. These components can be fed to the aircraft systems tocontrol the forward and VTOL propulsion systems of the aircraft. Actualvelocity can be measured and compared with (e.g., subtracted from) thedesired velocity to obtain a velocity error. The velocity error can beused to generate the forward thrust pseudo-control used to feed thesplitting function.

Before describing embodiments of the systems and methods in detail, itis useful to describe an example aircraft with which such systems andmethods can be used. FIG. 1 is a diagram illustrating an exampleunmanned vertical take-off and landing (VTOL) aircraft with which thetechnology disclosed herein may be implemented. FIG. 2 is a diagramillustrating an example unmanned aircraft system in including an exampleunmanned aircraft an example remote control system.

Referring now to FIG. 1, this example aircraft is a hybrid quadrotoraircraft having an airframe that includes fuselage 61, fixed left andright wings 62 and 63, a tail assembly or empennage 65. Also shown areleft and right tail boom supports (not numbered for clarity of theillustration), and left and right head boom supports. Left and rightwings 62 and 63 are fixed to fuselage 61 to form a fixed wing airframe.

Left wing 62 and right wing 63 are airfoils that produce lift tofacilitate aircraft flight. During flight, air passing over the wingcreates a region of lower-than-normal air pressure over top surfaces ofleft and right wings 62 and 63, with a higher pressure existing on thebottom surfaces of left and right wings 62 and 63. This results in a netupward force acting on left and right wings 62 and 63 to generate lift.Left wing 62 is applied to and extends from left side of fuselage 61 andright wing 63 is applied to and extends from right side of fuselage 61.Although not shown, a left aileron is pivotally retained at the rear ofleft wing 62 near its outer or distal extremity, and a right aileron ispivotally retained at the rear of right wing 63 near the outer or distalextremity of right wing 63.

Empennage 65 gives stability to the aircraft, and is located behind andin spaced-apart relation to the trailing extremity of fuselage 61. Inthis embodiment, empennage 65 is exemplary of a twin tail assembly ortwin tail empennage may include left and right vertical stabilizers 90,91, and a horizontal stabilizer 92 extending between left and rightvertical stabilizers. The left and right vertical stabilizers 90, 91extend upward from a rear of their corresponding left and right tailboom supports while the horizontal stabilizer 92 is retained betweenleft and right tail boom supports. Rudders, not shown, may be pivotallyretained on the trailing edge of left and right stabilizers 90, 91. Anelevator 97 is pivotally retained on a rear of horizontal stabilizer 92.

This example aircraft is a hybrid craft including separate rotors forforward and vertical thrust. Particularly, this example is a hybridquadrotor “X” configuration. Accordingly, this example illustrates aforward thrust rotor 85, which is mounted to the rear extremity offuselage 61 in front of empennage 65. Forward thrust rotor 85, whichprovides forward thrust to aircraft 50, is typically powered by aforward propulsion engine, sometimes referred to as a main engine. Thisexample uses a single forward thrust rotor mounted at the rear of thefuselage 61. However, the technology can be applied to aircraft usingone or multiple thrust rotors mounted at other positions.

The example aircraft also includes a VTOL propulsion system, or simply aVTOL system, to provide vertical thrust for vertical takeoff and landingoperations. This example is a quadrotor VTOL system including four VTOLthrust rotors 110 in a quadrotor “X” pattern for providing vertical liftand yaw control authority to the aircraft. In other applications, thetechnology disclosed herein may be applied to aircraft having adifferent quantity of VTOL thrust rotors, or thrust rotors at differentlocations. VTOL aircraft can include fixed-mount VTOL thrust rotors orpivot-mount VTOL thrust rotors. Forward thrust engines and verticalthrust engines can be internal combustion engines or electric motors ora combination of the two.

Referring now to FIG. 2, the example illustrated in FIG. 2 includes anunmanned aircraft 200 and a remote control system 202 for the aircraft200. In this example, aircraft 200 includes a VTOL propulsion system212, a forward propulsion system 216, various sensors 220, and onboardaircraft control system 222, and a command/telemetry interface 224.

VTOL propulsion system 212 includes systems and components used forvertical takeoff and landing. This can include, for example, one or morerotors, corresponding engines or motors, and other systems associatedwith VTOL propulsion. In various embodiments, the rotor or rotors ofVTOL propulsion system 212 are oriented horizontally or in anapproximately horizontal configuration. The rotor or rotors of VTOLpropulsion system 212 can be mounted in a fixed orientation, or can bemovably mounted such that their orientation can be adjusted from thehorizontal configuration. VTOL propulsion system 212 can include one ormore inputs to receive data, commands, control information, or otherinformation to operate or maintain the propulsion systems or componentsthereof. For example, a throttle control input can be provided to adjustthe throttle setting for the propulsion system. VTOL propulsion system212 can also include one or more outputs to send data and otherinformation about the propulsion system to other instrumentalities suchas, for example, onboard aircraft control system 222 or one or moresensors 220.

Forward propulsion system 216 includes one or more rotors, correspondingengines or motors, and other systems associated with forward propulsion.The rotor or rotors of forward propulsion system 216 are orientedvertically or in an approximately vertical configuration to provideforward or reverse thrust to the aircraft. The rotor or rotors offorward propulsion system 216 are generally mounted in a fixedorientation, but in some embodiments may be movably mounted such thattheir orientation can be adjusted from the vertical configuration.Forward propulsion system 216 can also include one or more outputs tosend data and other information about the propulsion system to otherinstrumentalities such as, for example, onboard aircraft control system222 or one or more sensors 220. Forward propulsion system 216 caninclude one or more inputs to receive data, commands, controlinformation, or other information to operate or maintain the propulsionsystems or components thereof. For example, a throttle control input canbe provided to adjust the throttle setting for the propulsion system.

Sensors 220 can include one or more various sensors to sense operatingparameters of the aircraft and its various systems and subsystems. Forexample, sensors 220 can include sensors such as temperature sensors,RPM sensors, airspeed sensors, altimeters, position determinationsystems (e.g. GPS or other position determination systems) vibrationsensors, gyros, accelerometers, and so on. Sensors can accordingly senseconditions or other operating parameters of aircraft 200 and its varioussystems and subsystems. Although illustrated as a single block in thisdiagram, sensors 220 can include individual discrete sensors disposed invarious positions about the aircraft to sense the appropriateparameters.

Command/telemetry interface 224 provides a communication interface toallow aircraft 200 to communicate, preferably two-way, with remotecontrol system 202. Accordingly, command/telemetry interface 224 caninclude an antenna and a communication transceiver to provide wirelesscommunications so they can receive command and control information fromremote control system 202 as well as send data or other telemetry toremote control system 202.

Onboard aircraft control system 222 is provided to control the variouscomponents of the aircraft based on commands received from remotecontrol system 202 (e.g., via the command/telemetry interface 224).Onboard aircraft control system 222 can also be configured to receiveinformation from other aircraft components such as, for example, sensordata, and provide that information to command/telemetry interface 224for transmission to remote control system 202.

Although the functional components of aircraft 200 (e.g., onboardaircraft control system 222, command/telemetry interface 224 andautomatic aircraft recovery system 240) are partitioned in this examplein the manner as illustrated in FIG. 2, it is noted that thispartitioning is done for clarity of description and by way of exampleonly. After reading this description, one of ordinary skill in the artwill understand how different architectures or alternative partitioningcan be used for systems of aircraft 200. Additionally, components suchas processing devices, memory components, communications buses and so oncan be shared among these multiple functional units. Indeed, in someapplications, for example, a single microprocessor (whether single ormulti-core) system can be used to implement the functions of onboardaircraft control system 222, and automatic aircraft recovery system 240,as well as portions command/telemetry interface 224, sensors 220, andeven digital/electronic portions of the various propulsion systems.

Remote control system 202 in this example includes a command/telemetryinterface 232, and aircraft control system 234 a control dashboard anduser interface 236 and an autopilot system 238. Command/telemetryinterface 232 provides a wireless communication interface to aircraft200. In some embodiments, remote control system 202 can be used tocommand multiple aircraft, in which case command/telemetry interface 232can provide a communication interface to multiple aircraft.

Control dashboard and GUI 236 provides a user interface to the remotepilot to allow the pilot to control one or more aircraft such asaircraft 200. Control dashboard and GUI 236 can be configured to providevisual, audible, and tactile feedback and information to the pilotregarding flight of the aircraft and various aircraft parameters. Youcan also include user input mechanisms to allow the pilot to control theaircraft remotely. These user input mechanisms can include, for example,buttons, switches, levers, joysticks, keys, touchscreen inputs, or otheractuators to enable the pilot to provide input and adjust aircraftsettings. This can allow the pilot to control, for example, throttlesettings for the various propulsion systems, to adjust the rudder andailerons, and so on.

Inputs from the user are interpreted by aircraft control system 234 totranslate user inputs into commands for aircraft control. In someapplications, this can be a translation of direct commands such asthrottle inputs, rudder control, flap adjustment and so on. Controlinputs can also include higher level commands such as rotation rate orrate over ground, etc., which can be translated into aircraft systemcontrol commands. These commands are communicated to aircraft 200 viacommand/telemetry interface 232 and command/telemetry interface 224.Functionality for aircraft control can be distributed among aircraftcontrol system 234 and onboard aircraft control 222 as may beappropriate depending on the system configuration.

An autopilot system 238 can also be provided to control the aircraft viacomputerized or automated control with little or no input required by ahuman pilot. Although illustrated in this example as part of remotecontrol system 202, part or all of the functionality of autopilot system238 can be provided at aircraft 200. Although not illustrated, in someembodiments an onboard autopilot system can be included with theaircraft 200 to enable local autopilot control, which may ease the loadon the command/telemetry interfaces.

Although the functional components of remote control system 202 (e.g.,aircraft control system 234, control dashboard and GUI 236, autopilotsystem 238, and command/telemetry interface 232) and aircraft 200 arepartitioned in this example in the manner as illustrated in FIG. 2, itis noted that this partitioning is done for clarity of description andby way of example only. After reading this description, one of ordinaryskill in the art will understand how different architectures oralternative partitioning can be used for aircraft 200 or remote controlsystem 202. Additionally, components such as processing devices, memorycomponents, communications buses, and so on can be shared among thesemultiple functional units. Indeed, in some applications, for example, asingle microprocessor (whether single or multi-core) system can be usedto implement the various described functions of remote control system202 (e.g., aircraft control system 234, and autopilot system 238, aswell as portions of control dashboard in GUI 236 and command/telemetryinterface 232) or aircraft 200.

Having thus described an example aircraft and unmanned aircraft systemwith which one or more aspects of the disclosed technology can beimplemented, various embodiments are now described. Although thedisclosed technology may be described from time to time herein in termsof this example aircraft, one of ordinary skill in the art reading thisdisclosure will understand how aspects of the disclosed technology canbe implemented with different aircraft and different aircraftconfigurations. This can include different configurations of unmannedaircraft as well as various configurations of manned aircraft.

FIG. 3 is a diagram illustrating an example process for combined thrustcontrol in accordance with one embodiment of the systems and methodsdescribed herein. FIG. 4 is a diagram illustrating an example controlloop for combined thrust control in accordance with one embodiment ofthe systems and methods described herein. With reference now to FIGS. 3and 4, at operation 410 the aircraft control system receives a forwardthrust control command. This command can be generated, for example,based on throttle position or based on desired aircraft speed (such asfrom an autopilot or like system). In the example illustrated in FIG. 4,the desired velocity 282 is compared to the actual velocity 289 togenerate a velocity error signal 284.

At operation 412, control system uses the velocity error signal 284 togenerate a forward thrust pseudo-control 285. The forward thrustpseudo-control 285 maps to a pitch angle for the aircraft that wouldnormally be used to command the VTOL rotors. Thus, the forward thrustpseudo-control 285 can also be referred to as a pitch-angle command tocontrol the pitch-angle of the aircraft to add forward velocity. PIDcontrol 262 can be implemented as a proportional-integral-derivative(PID) controller to provide the forward thrust pseudo-control in thetime domain where the forward thrust pseudo-control 285 is given by:

${PitchAngle} = {{K_{p}{e(t)}} + {K_{i}{\int{{e(t)}{dt}}}} + {K_{d}\frac{de}{dt}}}$

where the e represents the velocity error 284, and PID control 262computes both the derivative and the integral of this velocity error284. In this example, forward thrust pseudo-control 285 is given by theproduct of the proportional gain K_(p) and the magnitude of the velocityerror 284 plus the integral gain, K_(i), times the integral of thevelocity error 284 the derivative gain, K_(d), times a derivative of theerror. This allows the control signal to be generated based not only onthe current error but also one past error as well as the rate of changeof the error signal. In other embodiments, other controller types suchas PI, PD, P or I controllers can be used to generate the forward thrustpseudo-control.

At operation 414, the forward thrust pseudo-control signal 285 isdivided into a pitch angle command 287 and a forward thrust throttlecommand 286 by the splitting function 264. Splitting function 264evaluates the forward thrust pseudo-control 285 in light of a determinedmaximum pitch angle for the aircraft and generates the two new commandsignals, pitch angle command 287 and forward thrust throttle command286, based on the forward thrust needed and the determined maximum pitchangle. In other embodiments, Splitting function 264 evaluates theforward thrust pseudo-control 285 in light of a determined minimum pitchangle or in light of a range between a minimum and maximum pitch angle.

FIG. 5 is a diagram illustrating an example implementation of asplitting function 264 in accordance with one embodiment of the systemsand methods described herein. FIG. 6 is a diagram illustrating anexample process for determining pitch angle and forward thrust commandsin accordance with one embodiment of the systems and methods describedherein. Turning now to FIGS. 5 and 6, in this example at operation 426,a pitch limiter 324 receives the pitch angle command, forward thrustpseudo-control 285. At operation 428, pitch limiter 324 limits the pitchangle command to limit the amount of forward pitch and outputs this as anew limited pitch angle command 287. For example, the pitch anglecommand 287 may be limited such that the forward pitch of the aircraftdoes not exceed a predetermined maximum or a percentage of apredetermined maximum as determined at operation 424. The predeterminedmaximum can be set based on a maximum amount of negative lift for theaircraft, which can be a maximum for an aircraft or a maximum based oncurrent conditions. As another example, the pitch angle may be limitedto require a minimum amount of pitch or the pitch angle can be boundedto a limited range of pitch angles between determined minimum andmaximum pitch angles. The minimum and maximum pitch angles can bedetermined for the aircraft by an operator or aircraft designer andstored in memory. In other embodiments, minimum and maximum pitch anglescan be determined algorithmically and may in some applications varybased on weather or other flight conditions, payload restrictions orother parameters.

At operation 430, pitch limiter 324 computes the amount of forwardvelocity (e.g., airspeed) that will be generated by the limited pitchangle command 287. This can be an estimate of the airspeed based on theknown rotor configuration for the aircraft. At operation 432, pitchlimiter 324 computes the residual pseudo-control 336 needed beyond thatprovided by the limited pitch angle command to achieve the amount ofcontrol specified by forward thrust pseudo-control 285. This can beimplemented, for example, by computing the residual pitch angle as thedifference between the pseudo-command and the limited output.

At operation 434, the residual pseudo-control 336 a gain is applied bygain block 326 to converted this into a forward thrust throttle command286. Accordingly, splitting function 264 generates a modified pitchangle command 287 and a forward thrust throttle command 286 to controlthe VTOL rotors and the forward thrust rotor(s), respectively. In someembodiments, the system generates the forward thrust engine throttlecommand by determining a residual amount of forward thrust needed tocompensate for the reduced pitch angle command and generating theforward thrust engine throttle command to at least partially provide theresidual amount of forward thrust needed. As noted above, this can beaccomplished by generating a residual pitch angle command and convertingthe residual pitch angle command into a forward thrust throttle command.

Returning now to FIG. 3, at operation 416, the modified pitch anglecommand 287 is converted into VTOL rotor commands 288 for the VTOLrotors via control block 268. This function generates the commandsignals necessary to control the VTOL rotors to provide the pitch angledetermined. At operation 418, the forward thrust throttle command 286and VTOL rotor commands 288 are provided to their respective aircraftsystems to generate the indicated amount of thrust. The resulting actualvelocity of the aircraft after the application of these commands can bemeasured or estimated (e.g., via GPS or an airspeed sensor), an outputas an actual velocity signal 289. At this point, a new error signal 284can be computed by summing block 260 and the operation repeated.

The system configured to perform the functions for combined pitch andforward thrust control in accordance with the technology disclosedherein can be implemented on board the aircraft or at the remote controlsystem, or the functions can be distributed across these two platforms.The various subsystems or blocks described herein may be implementedutilizing any form of hardware, software, or a combination thereof.These may be further referred to herein as a processing block,processing module, or processor. A processing block, processing module,or processor may include, for example, one or more processors,controllers, central processing units, ASICs, PLAs, PALs, PLDs, CPLDs,FPGAs, logical components, or other mechanism or device that manipulatesor operates on signals, whether analog or digital, based on hard codingor wiring of the circuitry, the execution of operational instructions,or a combination thereof.

The processing block, processing module, or processor may furtherinclude, memory (separate, integrated or embedded from the one or moreprocessors), which may be include one or more memory devices. Such amemory device may include, for example, one or a combination of memorytypes such as read-only memory, random access memory, volatile andnon-volatile memory, static memory, dynamic memory, flash memory, cachememory, or other information storage device, whether magnetic, acoustic,optical or otherwise.

One or more processing devices may be centrally located or may bedistributed across locations (e.g., cloud computing via indirectcoupling via a local area network and/or a wide area network). Forexample, in implementation, the various subsystems or blocks describedherein might be implemented as discrete modules or the functions andfeatures described can be shared in part or in total among one or moreprocessing modules. In other words, as would be apparent to one ofordinary skill in the art after reading this description, the variousfeatures and functionality described herein may be implemented in anygiven application and can be implemented in one or more separate orshared processing modules in various combinations and permutations. Eventhough various features or elements of functionality may be individuallydescribed or claimed as separate subsystems or blocks, one of ordinaryskill in the art will understand that these features and functionalitycan be shared among one or more common software and hardware elements,and such description shall not require or imply that separate hardwareor software components are used to implement such features orfunctionality.

While various embodiments of the disclosed technology have beendescribed above, it should be understood that they have been presentedby way of example only, and not of limitation. Likewise, the variousdiagrams may depict an example architectural or other configuration forthe disclosed technology, which is done to aid in understanding thefeatures and functionality that can be included in the disclosedtechnology. The disclosed technology is not restricted to theillustrated example architectures or configurations, but the desiredfeatures can be implemented using a variety of alternative architecturesand configurations. Indeed, it will be apparent to one of skill in theart how alternative functional, logical or physical partitioning andconfigurations can be implemented to implement the desired features ofthe technology disclosed herein. Also, a multitude of differentconstituent module names other than those depicted herein can be appliedto the various partitions. Additionally, with regard to flow diagrams,operational descriptions and method claims, the order in which the stepsare presented herein shall not mandate that various embodiments beimplemented to perform the recited functionality in the same orderunless the context dictates otherwise.

Although the disclosed technology is described above in terms of variousexemplary embodiments and implementations, it should be understood thatthe various features, aspects and functionality described in one or moreof the individual embodiments are not limited in their applicability tothe particular embodiment with which they are described, but instead canbe applied, alone or in various combinations, to one or more of theother embodiments of the disclosed technology, whether or not suchembodiments are described and whether or not such features are presentedas being a part of a described embodiment. Thus, the breadth and scopeof the technology disclosed herein should not be limited by any of theabove-described exemplary embodiments.

Terms and phrases used in this document, and variations thereof, unlessotherwise expressly stated, should be construed as open ended as opposedto limiting. As examples of the foregoing: the term “including” shouldbe read as meaning “including, without limitation” or the like; the term“example” is used to provide exemplary instances of the item indiscussion, not an exhaustive or limiting list thereof; the terms “a” or“an” should be read as meaning “at least one,” “one or more” or thelike; and adjectives such as “conventional,” “traditional,” “normal,”“standard,” “known” and terms of similar meaning should not be construedas limiting the item described to a given time period or to an itemavailable as of a given time, but instead should be read to encompassconventional, traditional, normal, or standard technologies that may beavailable or known now or at any time in the future. Likewise, wherethis document refers to technologies that would be apparent or known toone of ordinary skill in the art, such technologies encompass thoseapparent or known to the skilled artisan now or at any time in thefuture.

The presence of broadening words and phrases such as “one or more,” “atleast,” “but not limited to” or other like phrases in some instancesshall not be read to mean that the narrower case is intended or requiredin instances where such broadening phrases may be absent. The use of theterm “module” does not imply that the components or functionalitydescribed or claimed as part of the module are all configured in acommon package. Indeed, any or all of the various components of amodule, whether control logic or other components, can be combined in asingle package or separately maintained and can further be distributedin multiple groupings or packages or across multiple locations.

Additionally, the various embodiments set forth herein are described interms of exemplary block diagrams, flow charts and other illustrations.As will become apparent to one of ordinary skill in the art afterreading this document, the illustrated embodiments and their variousalternatives can be implemented without confinement to the illustratedexamples. For example, block diagrams and their accompanying descriptionshould not be construed as mandating a particular architecture orconfiguration.

What is claimed is:
 1. An aircraft control system for an unmannedaircraft comprising a forward propulsion system comprising a forwardthrust engine and a vertical propulsion system comprising a verticalthrust engine, the aircraft control system comprising: a controllercomprising an input configured to receive a velocity signal indicating adetermined amount of forward velocity, the controller being configuredto generate a control signal associated with the determined amount offorward velocity; a splitting block comprising an input configured toreceive the control signal, the splitting block being configured togenerate a limited pitch angle command and a forward thrust enginethrottle command based on a bounded pitch angle for the unmannedaircraft; and an output configured to provide the limited pitch anglecommand to the vertical propulsion system and the forward thrust enginethrottle command to the forward propulsion system.
 2. The aircraftcontrol system of claim 1, wherein at least one of the controller,splitting block and the output are part of an onboard aircraftcontroller.
 3. The aircraft control system of claim 1, wherein at leastone of the controller, splitting block and the output are part of anaircraft control system of a remote control system.
 4. The aircraftcontrol system of claim 3, wherein the limited pitch angle command andthe forward thrust engine throttle command are sent to the verticalpropulsion system and the forward propulsion system, respectively, viawireless communication transceivers.
 5. The aircraft control system ofclaim 3, wherein at least one of the controller, splitting block and theoutput are part of both an onboard aircraft controller and the aircraftcontrol system of the remote control system.
 6. The aircraft controlsystem of claim 1, wherein the unmanned aircraft is a multirotoraircraft and the vertical propulsion system comprises a plurality ofvertical thrust engines and corresponding rotors.
 7. The aircraftcontrol system of claim 1, wherein the unmanned aircraft is a hybridmultirotor aircraft.
 8. The aircraft control system of claim 1, whereinthe bounded pitch angle comprises a maximum pitch angle.
 9. The unmannedaircraft system of claim 1, wherein the bounded pitch angle comprises arange of pitch angles between a minimum pitch angle and a maximum pitchangle.
 10. The unmanned aircraft system of claim 1, wherein thedetermined amount of forward velocity comprises a velocity error betweena desired aircraft velocity and an actual aircraft velocity.
 11. Theunmanned aircraft system of claim 1, wherein forward thrust engine andthe vertical thrust engine of the unmanned aircraft each comprise aninternal combustion engine or a motor.
 12. The aircraft control systemof claim 1, wherein the control signal comprises a pitch angle commandto control the pitch angle of the unmanned aircraft to add forwardvelocity.
 13. The aircraft control system of claim 1, wherein thecontrol signal comprises a forward thrust pseudo-control that maps to apitch angle of the unmanned aircraft to increase forward velocity of theunmanned aircraft.
 14. The aircraft control system of claim 13, whereinthe forward thrust pseudo-control is based on a magnitude of a velocityerror between a desired aircraft velocity and an actual aircraftvelocity.
 15. The aircraft control system of claim 1, wherein thelimited pitch angle command is generated such that a resultant forwardpitch of the unmanned aircraft does not exceed the bounded pitch anglefor the unmanned aircraft.
 16. The aircraft control system of claim 1,wherein the limited pitch angle command is generated such that aresultant forward pitch angle of the aircraft does not exceed thebounded pitch angle for the unmanned aircraft and the forward thrustengine throttle command is generated to provide additional thrust to, incombination with the resultant forward pitch angle, achieve thedetermined amount of forward velocity.
 17. The aircraft control systemof claim 1, wherein the splitting block comprises a pitch limiter andwherein the pitch limiter is configured to compute an amount of forwardvelocity to be generated by the limited pitch angle command.
 18. Theaircraft control system of claim 17, wherein the pitch limiter isfurther configured to compute a residual pitch angle as a differencebetween a velocity generated by the limited pitch angle command and thedetermined amount of forward velocity.
 19. The aircraft control systemof claim 18, wherein the splitting block further comprises a gain blockconfigured to apply a gain to the residual pitch angle to generate theforward thrust engine throttle command.
 20. The aircraft control systemof claim 18, wherein the splitting block further comprises a gain blockconfigured to determine a residual amount of forward thrust needed tocompensate for the limited pitch angle command and generate the forwardthrust engine throttle command to at least partially provide thedetermined residual amount of forward thrust.
 21. The aircraft controlsystem of claim 1, further comprising an onboard aircraft controllercomprising a first output coupled to the forward propulsion system and asecond output coupled to the vertical propulsion system.
 22. Theaircraft control system of claim 1, further comprising a control blockto convert the limited pitch angle command into a vertical thrust enginecommand.
 23. The aircraft control system of claim 1, wherein the boundedpitch angle is determined based on flight conditions.
 24. The aircraftcontrol system of claim 1, wherein the signal indicating a determinedamount of forward velocity comprises a velocity error signal indicatinga difference between an actual velocity of the unmanned aircraft and adesired velocity of the unmanned aircraft.
 25. An unmanned aircraft,comprising: a forward propulsion system comprising a forward thrustengine and a first rotor coupled to the forward thrust engine; avertical propulsion system comprising a vertical thrust engine and asecond rotor coupled to the vertical thrust engine; and a pitch angleand throttle control system, comprising: a controller comprising aninput configured to receive a velocity signal indicating a determinedamount of forward velocity, the controller being configured to generatea pitch angle command associated with the determined amount of forwardvelocity; a splitting block comprising a splitting block inputconfigured to receive the pitch angle command, the splitting blockconfigured to generate a limited pitch angle command and a forwardthrust engine throttle command based on a bounded pitch angle for theaircraft; and an output configured to provide the limited pitch anglecommand to the vertical propulsion system and the forward thrust enginethrottle command to the forward propulsion system.
 26. An unmannedaircraft system, comprising: an unmanned aircraft comprising a pitchangle and throttle control system, the pitch angle and throttle controlsystem comprising a processor configured to: receive a first pitch anglecommand, the first pitch angle command generated by a remote control;compare a first aircraft pitch angle corresponding to the first pitchangle command to a bounded pitch angle for the aircraft; generate asecond pitch angle command so a second aircraft pitch anglecorresponding to the second pitch angle command does not exceed thebounded pitch angle; and generate a forward thrust engine throttlecommand based on the second pitch angle command; and the remote controlsystem communicating with the communicate with the unmanned aircraft,the remote control system comprising a processor configured to: receivea velocity signal indicating a determined amount of forward velocity andbeing configured to generate the first pitch angle command associatedwith the determined amount of forward velocity.
 27. An unmannedaircraft, comprising: a pitch angle and throttle control system,comprising a processor configured to: receive a first pitch anglecommand and to generate a second pitch angle command and a forwardthrust engine throttle command based on a bounded pitch angle for theaircraft; compare the bounded pitch angle for the aircraft to a firstaircraft pitch angle corresponding to the first pitch angle command;generate the second pitch angle command so a second aircraft pitch anglecorresponding to the second pitch angle command does not exceed thebounded pitch angle; generate a residual pitch angle command based on adifference between the first pitch angle command and the second pitchangle command; and convert the residual pitch angle command into theforward thrust engine throttle command, wherein the residual pitch anglecommand is of a magnitude estimated to provide a residual amount offorward thrust to compensate for the difference between the first pitchangle command and the second pitch angle command.